1. Field of the Invention
The present invention relates to a method for assembling a polishing head and an apparatus for detecting air leakage in the polishing head while assembling the same. More particularly, the present invention relates to a method for assembling a polishing head while inspecting each tube of the polishing head for air leakage and an apparatus suitable for performing the method.
2. Description of the Related Art
Semiconductor technology is making great strides as information media such as computers are becoming more widely used. In a functional aspect, a semiconductor device is required to be operated at a high speed with a large storage capacity. Accordingly, semiconductor technology is developed to improve the degree of integration, the reliability, and the response speed of semiconductor devices. Therefore, micro-processing techniques are governed by strict requirements in order to improve the degree of integration of semiconductor devices.
Among the micro-processing techniques for improving the degree of integration of semiconductor devices is a planarization technique. In the semiconductor manufacturing industry, chemical mechanical polishing (CMP), in which a wafer is directly polished, is primarily used as a planarization technique.
In order to evenly planarize a wafer using the CMP process, it is important that uniform pressure is applied to each part of the wafer during the CMP process. Accordingly, it is important to provide a proper polishing head, which grips the wafer (holds the wafer by applying suction to the wafer) thereby applying pressure to the wafer during the CMP process.
Specifically, an inner portion of the polishing head has a plurality of tubes used for air passage. A pneumatic pressure or a vacuum is supplied through the tubes. At this time, the wafer below the polishing head is pushed towards a polishing pad by the pneumatic pressure supplied to the polishing head, so that a contact-pressure between the wafer and the polishing pad increases. In addition, the wafer is gripped by suction at a lower portion of the polishing head by the vacuum supplied to the polishing head. However, if there is any air leakage in the tubes of the polishing head, the predetermined pneumatic pressure or the predetermined vacuum cannot be normally supplied to the polishing head. In such a case of air leakage in the tubes, the wafer is unevenly polished due to non-uniform pressure, or the wafer falls from the polishing head due to insufficient suction.
The prior art discloses a polishing device including a polishing head having an air line for controlling the operation of the polishing head and an air control system for controlling the polishing head. The air control system inspects for air leakage in the air line of the polishing head installed in the polishing device. In addition, the prior art discloses a polishing head capable of checking for the existence of a wafer by detecting a pressure variation.
The polishing head has to be periodically disassembled for cleaning or exchanging parts thereof. After being re-assembled, the polishing head is installed in the polishing device. If the polishing head is incorrectly assembled, the pneumatic pressure or the vacuum supplied to the polishing head leaks therefrom, so that the polishing head is unable to grip the wafer or the wafer does not receive a precise pressure. Therefore, after assembling the polishing head, testing the polishing head for the existence of air leakage is required. Only if the polishing head does not generate any air leakage can it be used in the CMP process.
The test method is as follows. Firstly, the assembled polishing head is installed in the polishing device. Then, the CMP process, in which a wafer is gripped by the polishing head, is carried out using a dummy wafer. Thereafter, a surface of the polished dummy wafer is inspected to detect scratches and particles formed thereon, thereby determining whether or not the dummy wafer is normally polished. Upon completion of the test, if the dummy wafer is normally polished, a wafer for manufacturing a semiconductor device is introduced into the polishing device equipped with the polishing head, and the CMP process is carried out with respect to the wafer.
If the dummy wafer is abnormally polished, a user separates the polishing head from the polishing device in order to disassemble and re-assemble the polishing head. Then, after re-assembling the polishing head, the leakage test must again be carried out using a dummy wafer to test the polishing head. The leakage test takes about 6 hours. Since about 10% of assembled polishing heads have some air leakage, it is necessary to re-assemble the polishing heads about 10% of the time, resulting in a marked reduction in production from the polishing device. Accordingly, productivity of the semiconductor device manufacturing equipment is also lowered.